The invention relates to a video sequential color system, and more particularly, to a miniature, compact and lightweight color camera system.
Video color camera systems require at least three independent video signals, such as red blue and green for transmission of a color scene. Early systems required three image sensing devices (vidicon tubes) to generate the red, blue and green information signals for processing the color image of the scene.
Field sequential color systems are generally well known and involve the use of a single image sensing device which sequentially receives the red, blue and green color information at a high cycle rate. These signals are stored and processed for color transmission. Sequential systems require that the signals be separated into at least three independent spectral regions, usually red blue and green.
Some systems utilize a series of striped filters, such as red, blue and green, positioned over the viewing surface of the image sensing device to separate the image into three spectral regions. A problem with the striped filter systems is that the information received by each color region is only over 1/3 of the image sensing surface which greatly reduces the clarity or resolution of the image.
Other sequential systems utilize a series of dichroic mirrors, or rotating color filter wheels, or three high frequency colored strobe lights to sequentially illuminate the scene and to separate the signals into three independent spectral regions. One such representative prior art system is shown in U.S. Pat. No. 4,253,447 issued Mar. 3, 1981 to Moore et al. This patent describes a color endoscope having a single CCD image sensing device with three colored light sources to sequentially illuminate an object to be televised. The full resolution signals from the CCD are stored in analog CCD memory banks for processing into standard broadcast format. Typical prior art systems utilize a three color primary color system of red, blue and green and process the full resolution signals.
Video color signals are functions of numerous components. The major components include a luminance component representing the brightness or intensity of the scene being televised, and three or more color or chroma components. The signals from the image sensing device are referred to as full resolution read-out signals. The full resolution luminance signals are required for every picture element for high resolution transmission. The luminance signals cover a bandwidth of about 3 MHz and require a sampling rate of about 6 MHz. This corresponds to 244 lines of picture height, with 320 horizontal picture elements, and a six bit identification code for a total of about 468K bits (244.times.320.times.6) of data storage capacity for each field scan of the image sensing device.
The present invention recognizes that the chroma component information signals have properties which are relatively lower in acuity and perceptibility by the human eye than are the luminance components. These lower acuity properties permit the chroma information to be identified by a much lower sampling rate, without any noticable degradation in resolution to the human eye. The chroma signals can therefore be processed as low resolution signals having a bandwidth of about 0.5 MHz and a sampling rate of 1 MHz. This corresponds to 40 lines with 50 elements having a four bit identification code for a total of 8K bits (40.times.50.times.4) of data storage capacity for each scan of the image sensing device.
The present invention also recognizes two basic color principles. One basic principle is that two complementary colors add to neutral. Another basic principle is that three independent chroma signals are defined to add to zero. A third chroma signal can therefore always be found as the negative of the sum of the other two signals.
By utilizing the properties of low acuity chroma signals, complementary addition to neutral, and three chroma addition to zero, field sequential color signal processing can be uniquely and significantly simplified.